The invention relates to a fuel injection pump for internal combustion engines as defined hereinafter. Injection pumps in which there is a separate pumping element for each engine cylinder and in which these pump elements are disposed in a row are called in-line injection pumps; they have come into extremely widespread use, especially in self-igniting or so-called Diesel engines. Technological development in such engines is directed to optimizing the course of combustion, in order to meet increasingly stringent exhaust gas regulations, and to reducing the specific weight-to-power ratio. With greatly increased injection pressures, the metered fuel quantity must be very uniform and accurate for each individual pumping element. The fuel metering is effected such that the portion of the fuel that does not result in being injected returns at high pressure into the interior of a collecting chamber of the injection pump. The overflowing of the fuel, which is at high pressure at pump piston control edges causes the fuel to heat up, and hence such physical properties as density and compressibility vary as well, so that both the quantity of fuel metered per pump stroke and its thermal energy content vary, which causes uniform performance by the engine cylinders. For instance, in a high-pressure injection pump designed for a peak pressure of 1200 bar, and with a full-load injection quantity of 150 mm.sup.3 per stroke, the result is a return flow quantity 750 mm.sup.3 per storke, comprising the diverted fuel quantity plus an overflow quantity returning during the pre-stroke. This heated fuel mixes with the inflowing cold fuel; with conventional injection pumps having a common suction chamber for all the pumping elements, the above-described disadvantages are the result.
In a fuel injection pump of this generic type, known from German Offenlegungsschrift No. 25 47 071, the common suction chamber from which all the pumping elements of the in-line injection pump pump the fuel that is to be metered has already been subdivided into a plurality of partial suction chambers, each of which is associated with one pumping element. Each partial suction chamber has a throttle connection with a common outflow conduit and is supplied from a common inflow conduit. In this known fuel injection pump, however, the outflowing fuel emerging at high pressure and hence heated thereby cannot be prevented from mixing with inflowing fuel in the common inflow conduit, thus causing uncontrollable deviations in the fuel quantities metered in the combustion chambers of the engine.
In order to overcome this disadvantage, the patent application on which German Offenlegungsschrift No. 33 26 045 is based has proposed embodying the partial suction chambers in the form of a hollow cavity entirely surrounding the pump cylinders and communicating with the return flow conduit only via the return flow opening and with the inflow conduit via a throttled inflow opening. The flowthrough cross section of the throttled inflow openings was smaller than the flow-through cross section of the associated return flow openings. Since the heat of the pumping elements and partial suction chambers is also transmitted to the pump housing, the inflowing fuel already heats up while on the way through the pump housing, before reaching the partial suction chambers. The fuel thus assumes ever increasingly higher temperatures as it passes through the pump. This is a further source of errors in fuel quantity, especially because of the influence of temperature when the load point (that is, the quantity of fuel to be injected) is changing. To lessen fuel quantity errors, the following demands were made of the suction chamber system:
Since it is unavoidable that the temperature in the partial suction chambers is dependent on the load point or in other words is not constant, the same temperature should be attained in all of the partial suction chambers;
the modulation behavior of the temperature should be the same for all partial suction chambers;
in the individual partial suction chambers, the flow of heat drawn off with the aid of the scavenging quantity should be of equal magnitude; and
the temperature of the pump housing should be at an equal level at each pumping element.